The present invention relates to a polyorganosiloxane composition. More particularly, the invention relates to a room temperature curable polyorganosiloxane composition which is stable under moisture free, hermetically closed conditions and which cures upon contact with water contained in air at room temperature to form an elastomer.
Among polyorganosiloxane compositions which cure at room temperature to form elastomers, one-package types which cure upon contact with water contained in the air have been used widely as elastic adhesives or coating agents in the electrical and electronic industries. Also such compositions have been used as sealants in the construction industry since they necessitate no troublesome step of weighing the same, a crosslinking agent and/or a curing catalyst, or mixing them together and, therefore, no failures are caused in these steps and they have excellent contact properties.
These compositions comprise a silanol terminated polydiorganosiloxane and a crosslinking agent having more than two hydrolyzable groups. Upon curing, they release acetic acid, a long-chain carboxylic acid, organic amine, amide, organic hydroxylamine, oxime compoud, alcohol or acetone depending on the crosslinking agent used.
A composition which releases acetic acid upon curing has quite excellent adhesion and curing properties. However, it has a problem of environmental hygiene due to the irritative smell thereof. Further, when it is applied to metals, a measure to counter its corrosiveness is required. A composition which releases a long-chain carboxylic acid has a problem in that rusting of metals, particularly after immersion in water, cannot be prevented easily, though it has no irritative smell. A composition which releases an amine has the problem that the amine formed is odorous and toxic. Compositions which release hydroxylamine, oxime or amide have problems in that they rust metals, particularly copper and its alloys. Though a composition which releases acetone cures rapidly and has no corroding property, it has the problems that a crosslinking agent contained therein cannot be synthesized easily and it turns yellow during storage.
A composition which releases an alcohol has the advantages that an alkoxysilane used as the crosslinking agent is available at a low cost, the released substance is an alcohol, such as methanol or ethanol, which is easily volatilized and no odor or corrosion problem is caused. However, compositions of this type have defects in that they set slowly and that the crosslinking agent is hydrolyzed by a very small amount of water contained therein during storage to form an alcohol which causes cracking of the base polymer to make the storability poor. Thus it is desirable to overcome these defects, particularly in the electrical and electronic industries, where room temperature curable polyorganosiloxane compositions are frequently used as an adhesive or coating material. The curable composition sometimes is cured in contact with copper or its alloy to form an elastomer. Similarly, compositions releasing an oxime, acetone or alcohol have been used and it is also necessary to overcome the above-mentioned defects in them.
Recently a room temperature curing polyorganosiloxane composition of the one-package type comprising a polydiorganosiloxane having an alkoxyl group bonded to the terminal silicon atoms, an alkoxysilane, a curing catalyst and an alcohol scavenger has been found. This composition has a high storage stability and rapid curing properties. It has also been found that when a compound containing a silicon-nitrogen bond which forms a non-volatile nitrogen-containing compound upon reaction with an alcohol is used as the alcohol-scavenger, no corroding effect is made on copper or its alloy.
Though the fast-cure, room temperature curable polyorganosiloxane composition which does not rust copper or its alloy is useful as an adhesive or coating material in the electric and electronic industries, the elastomer obtained has defects in that cracks are formed on its surface and its physical properties and durability are reduced. This appears to be because the compound containing silicon-nitrogen bonds used as the alcohol scavenger is hydrolyzed to form a hydrolyzate, which oozes out to the surface to resinify the surface.
After intensive investigations made for the purpose of producing a fast curing room temperature curable polyorganosiloxane composition free from the resinification of the silicone elastomer surface or corrosion, and capable of maintaining the elasticity of the surface after curing, the present inventors have found that a compound containing a polyoxyalkylene chain in its molecule is effective for the prevention of the resinification. The present invention has been completed on the basis of this finding.